Hands-free telephone apparatus

Abstract

Digital-type hands-free telephone apparatus is provided including a microcontroller, an audio board and a COFIDEC circuit, in which the microcontroller permanently calculates the average values of 16 successive samples on each one of the send and receive channels and deduces therefrom which channel is to be enabled while attenuating the other using tables provided in ROM memory.

What is claimed is: 
     
       1. Digital hands-free telephone apparatus for reception and transmission of digital speech data, said apparatus comprising: a microcontroller for processing digital data and having a receive input and a receive output associated with a receive channel, and a send input and a send output associated with a send channel,   a coding-filtering-decoding circuit for converting analog speech data into digital speech data and vice-versa,   a microphone and a loudspeaker coupled by respective send and receive amplifier circuits and by said coding-filtering-decoding circuit o the send input and ht receive output of the microcontroller, respectively,   decision means associated with said microcontroller for determining average levels over a predetermined number of successive digital samples of any signals present at the respective send and receive inputs to said microcontroller, and for using said average levels to perform a decision-making operation in which it is determined which channel should be processed without attenuation and which channel should be attenuated,   at lest one attenuated value table for determining an attenuated output value form a given input value,   digital attenuation means also associated with said microcontroller and responsive to said decision means and to said attenuated value table or deriving an attenuated microcontroller output for the channel to be processed with attenuation from its respective microcontroller input, and for deriving a non-attenuated microcontroller output for the other channel from the other microcontroller input, and   end-of-word detecting means for maintaining the average level between two successive words in order to prevent sudden channel switching between the words of a given phrase,   wherein the decision to switch from attenuation to non-attenuation and vice-versa is taken as a unction of a position of a point that represents, in Cartesian coordinates, the values of the average levels of the send and receive channels in three areas including a hysteresis area separating an area in which the transmit channel is not attenuated and an area in which the receive channel is not attenuated.   
     
     
       2. Telephone apparats according to claims 1, wherein said predetermine number of successive samples is equal to sixteen. 
     
     
       3. Telephone apparatus according to claim 1, wherein the area where the average level is low, two threshold values define a different in processing mode of the decision-making operations. 
     
     
       4. Telephone apparatus according to claim 3, wherein said decision means implements the following channel switching procedure: sampling levels of the send and receive inputs;   calculating send and receive averages of the thus sampled levels;   determining whether the thus calculated average levels correspond to a point within the low level area defined by said two threshold values;   then, if the answer is YES: a) if said receive average is greater than twice the send average plus one, a receive mode is enabled by not attenuating the receive channel and a send mode is inhibited by applying attenuation to the send channel, or   b) if said send average is greater than four times the receive average plus five, the send mode is enabled by not attenuating the send channel, and the receive mode is inhibited by applying attenuation to the receive channel, or   c) if said receive average is not greater than twice the send average plus one and said send average is not greater than four times the receive average plus five, any currently enabled mode remains enabled and any currently inhibited mode remains inhibited;   otherwise carrying out steps a) or b) or c) but with "twice the send average plus one" replaced by "twice the send average" and "four times the receive average plus five" replaced by "six times the receive average".